The oil-in-water type emulsion technology is widely used in producing photographic light-sensitive materials, cosmetics, foods, paints and chemicals.
For example, in the field of photographic light-sensitive materials, color image-forming compounds such as color couplers, diffusion transfer compounds, antistain agents, anti-discoloration agents, anti-color-mixing agents, ultraviolet absorbing agents, color-increasing agents and the like are used as oil-soluble substances for making their emulsions. The preparation of oil-in-water type emulsions of such oil-soluble substances has conventionally been made in the manner that an oil phase solution prepared by dissolving the oil-soluble substance in an organic solvent or emulsification aid or in an organic solvent solution of an emulsification aid or, where the oil-soluble substance is solid, by heating or dissolving it in an organic solvent (hereinafter merely called an oil phase solution) is added to be emulsified/dispersed in a water-soluble binder-containing and as needed an emulsification aid-added water phase solution (hereinafter merely called a water phase solution) to thereby produce an oil-in-water type emulsion having an average oil globular size of about 0.1 to 1.0 .mu.m.
As the above organic solvent, in many cases, a low-boiling solvent having a lower boiling point than that of water, such as ethyl acetate, is used.
A conventional procedure for the above emulsion preparation is such that the water phase solution is put in a stirrer-provided emulsification tank, and onto the surface of the solution, with stirring, is added the oil phase solution.
In addition, there are other procedures: addition by conduction of the oil phase into the water phase solution as disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter abbrebiated to JP O.P.I.) No. 203632/1984; and conduction of the water phase into the oil phase solution to the contrary. These procedures, however, have difficulty in securely adding all the amount of one phase solution to the other because, when forcibly conducting the adding phase by, e.g., a pump, there is a possibility of undesirable air-mixing at the end of the conduction, in which the air-mixing occurrence causes a large amount of foam, giving additional troubles to work.
Therefore, the foregoing addition of the oil phase onto the surface of the water phase solution is generally used. In this instance, however, the oil phase solution is splashed up onto the inside wall of the emulsification tank, the oil phase substance, after the emulsification, is dripped from the wall to be mixed in the dispersion, resulting in coarse oil globules of the undispersed oil phase substance which, when the dispersion is used in, e.g., a light-sensitive material, may sometimes cause coating trouble such as pinholes.